Airbag device for a driver's seat

Abstract

An airbag device includes a steering wheel a rim portion of which has a longer length in a left and right direction than in a front and back direction, and an airbag mounted on a boss section of the steering wheel. An outer shell of the airbag includes a vehicle-side wall that is configured to be supported by an upper surface of the rim portion when deployed, and a driver-side wall a central region of which is configured to deploy generally vertically for receiving the driver. The airbag as deployed includes, in a rear portion of the vehicle-side wall, a locking inflatable portion that protrudes downward from a vicinity of the upper surface of the rim portion of the steering wheel to be locked by a rear surface of the rim portion and prevent a front portion of the airbag from slipping forward.

What is claimed is: 
     
       1. An airbag device for a driver's seat, comprising:
 a steering wheel that is adapted to be mounted on a vehicle in such a manner that a central axis of rotation of the steering wheel extends obliquely rearwardly and upwardly, the steering wheel including: 
 a rim portion configured for gripping, the rim portion being disposed in an outer circumferential edge of the steering wheel apart from the central axis of rotation, the rim portion as viewed from above having such a shape that a length in a left and right direction is greater than a length in a front and back direction; and 
 a boss section that is disposed in a vicinity of the central axis of rotation; and 
 the airbag device is mounted on the boss section of the steering wheel for protecting a driver, the airbag device including an airbag that is configured to be deployed from the boss section and supported by an upper surface of the rim portion, 
 wherein an outer shell of the airbag includes: 
 a vehicle-side wall that is configured to be supported by the upper surface of the rim portion when deployed, the vehicle-side wall being greater than the rim portion in outside dimension in the front and back direction and in the left and right direction, the vehicle-side wall including, in a vicinity of a center thereof, an inlet port for introducing an inflation gas, and a mounting seat which is disposed in a periphery of the inlet port and by which the airbag is mounted on the boss section; and 
 a driver-side wall for receiving the driver, the driver-side wall extending from an outer circumferential edge of the vehicle-side wall and covering the inlet port; 
 wherein the airbag is configured to be inflated in such a fashion that a front portion thereof above the rim portion has a greater thickness than a rear portion thereof in order that a central region of the driver-side wall is deployed generally vertically; and 
 wherein the airbag as deployed further includes, in a rear portion of the vehicle-side wall, a locking inflatable portion that protrudes downward from a vicinity of the upper surface of the rim portion to be locked by a rear surface of the rim portion and prevent the front portion of the airbag from slipping forward. 
 
     
     
       2. The airbag device of  claim 1 , wherein:
 in order to be brought into contact with the upper surface to a rear surface of a rear end portion of the rim portion, the locking inflatable portion of the airbag as fully deployed has a shape of such a halved circular cone that a bottom plane faces upward and a division surface, which is taken along a height of the cone, faces forward; and 
 the locking inflatable portion includes, in a side facing forward, a locking surface that is configured to extend from an upper edge to a lower edge of the rear surface of the rim portion and be locked by the lower edge of the rear surface of the rim portion. 
 
     
     
       3. The airbag device of  claim 2 , wherein:
 the outer shell of the airbag is composed of a driver-side base cloth for forming the driver-side wall, and a vehicle-side base cloth for forming the vehicle-side wall; 
 the vehicle-side base cloth includes a front-side component for forming a front region of the vehicle-side wall, and a rear-side component that is connected to a rear portion of the front-side component and includes a region forming the mounting seat; 
 the rear-side component as developed has a generally circular shape; 
 the rear-side component includes a rear cut-out portion that is triangular and extends forward from a rear edge of the rear-side component, and two U-shaped cut-out portions that extend towards a center of the rear-side component along a left and right direction from left and right edges of a region of the rear-side component farther rearward than the mounting seat; 
 opposite edges of the rear cut-out portion are sewn together to close the rear cut-out portion, and opposite edges of each of the U-shaped cut-out portions are sewn together to close the U-shaped cut-out portion with a seam allowance disposed on an outer surface of the airbag; and 
 a straight line that connects outer ends of seams closing the left and right U-shaped cut-out portions is positioned in a vicinity of the rear end portion of the rim portion of the steering wheel at airbag deployment. 
 
     
     
       4. The airbag device of  claim 1 , wherein:
 the airbag further includes, at a vicinity of a center in a left and right direction of and inside of a rear end region thereof, at least one long tether and at least one short tether each of which connects the driver-side wall and vehicle-side wall, the long tether being longer than the short tether; 
 a joint portion of the long tether to the vehicle-side wall and a joint portion of the short tether to the vehicle-side wall are arranged one behind another in the vehicle-side wall; 
 a joint portion of the long tether to the driver-side wall and a joint portion of the short tether to the driver-side wall are arranged one behind another in the driver-side wall; 
 the joint portions of the long tether and short tether to the vehicle-side wall are configured to be located in a vicinity of a rear end portion of the rim portion of the steering wheel at airbag deployment; 
 both of the joint portions of the long tether and short tether to the driver-side wall are located farther rearward than the joint portions of the long tether and short tether to the vehicle-side wall; 
 in the driver-side wall, the joint portion of the short tether is located farther rearward than that of the long tether; 
 a distance between the joint portion of the long tether and that of short tether to the driver-side wall is greater than a distance between the joint portion of the long tether and that of the short tether to the vehicle-side wall; 
 a difference between the lengths of the long tether and short tether, and a difference between the distance between the joint portion of the long tether and that of short tether to the driver-side wall and the distance between the joint portion of the long tether and that of the short tether to the vehicle-side wall help deploy the locking inflatable portion to wrap around the rear end portion of the rim portion from the rear surface to a lower surface and be locked by the rear end portion of the rim portion at airbag deployment. 
 
     
     
       5. The airbag device of  claim 4 , wherein the joint portion of the long tether and the joint portion of the short tether to the vehicle-side wall are located at a same position, and thus the distance between the joint portions in the vehicle-side wall is zero. 
     
     
       6. The airbag device of  claim 4 , wherein:
 two long tethers and two short tethers are provided; and 
 the two long tethers and the two short tethers are each located at a distance from each other on both sides of a vicinity of the center in the left and right direction of the airbag. 
 
     
     
       7. The airbag device of  claim 4 , wherein:
 the outer shell of the airbag is composed of a driver-side base cloth for forming the driver-side wall, and a vehicle-side base cloth for forming the vehicle-side wall; 
 the driver-side base cloth includes, in a region farther rearward than a center in a front and back direction of the driver-side base cloth and farther forward than the joint portion of the long tether, a pleated portion that is formed on a plurality of creases which extend in the left and right direction; and 
 the driver-side base cloth as provided with the pleated portion and the vehicle-side base cloth are sewn together by outer circumferential edges thereof. 
 
     
     
       8. The airbag device of  claim 4 , wherein:
 the airbag further includes, on an outer surface of a vicinity of a center in a left and right direction of a rear region of the vehicle-side wall, an outer tether that connects a position in a vicinity of a rear end of the vehicle-side wall and a position rearward of the inlet port and forward of the joint portion of the short tether to the vehicle-side wall; and 
 a length of the outer tether is such as to bend a rear end region of the vehicle-side wall towards the inlet port when the airbag is inflated by itself. 
 
     
     
       9. The airbag device of  claim 4 , wherein:
 the airbag further includes s a bulkhead that is joined to inner surfaces of the driver-side wall and vehicle-side wall by outer circumferential edge thereof and divides the airbag into a chamber located towards a rear end of the airbag and a chamber located towards the inlet port; 
 the bulkhead concurrently acts as the long tether; and 
 the bulkhead includes a check valve that permits a flow of inflation gas through it to the rear end of the airbag but restricts a reverse flow.